Arizona Instrument LLC 3375 N. Delaware St. | Chandler, AZ 85225 Tel: (800) 528-7411 | Fax: (602) 281-1745 [email protected]Moisture Contamination and its Effect on the Remaining Useful Life of Bearings Determination and Analysis of Water Content in Lubricating Oils by RH Sensor G. Rowe, Q. Biamonte Arizona Instrument LLC Lubrication is Essential for Predictive and Preventative Maintenance Lubrication reduces friction, minimizes wear and tear on moving parts, decreases the likelihood that particle contamination will occur and helps maintain lower operating temperatures, all of which helps keep your machinery in optimum operation condition and extend its useful life. Lubrication is particularly important in regard to bearings. Bearings are the joints of a machine. They bear heavy loads and help execute and control the movement of the connected parts. When these joints fail, movement becomes less fluid and efficient and can eventually cause serious damage. Lubrication is a machine’s method of protecting its joints and ensuring that the machine as a whole is in good working order. It creates a barrier between the softer material of the bearings and the other parts of the machine. This helps defend the bearings against the excessive wear and tear that can dramatically reduce their useful life. When something threatens the potential effectiveness of lubrication, it not only affects the lubricant itself, but also the bearings and other moving parts that it was meant to protect. While each lubricant is designed with a specific purpose and application in mind, they all share a common nemesis: moisture contamination. This paper will discuss the dangers of moisture contamination, its effect on bearing life and the various techniques available for moisture analysis. Different Bearings Require Different Types of Lubrication The most common methods of lubrication associated with bearings are hydrodynamic and elastohydrodynamic. [2] An understanding of how these types of lubrication work will help demonstrate the important role that lubrication plays in ensuring that your machinery continues to run smoothly. Both hydrodynamic and elastohydrodynamic lubrication use the motion of moving machinery parts to force the lubricant around or between those moving parts. [4] In hydrodynamic lubrication specifically, the lubricant is pushed up and around the bearing, surrounding it in a thin layer of oil. The continued motion of the machinery allows for a constant flow of lubricating oil, creating a protective layer that is always intact. Fig. 1 Hydrodynamic Lubrication
Moisture Contamination and its Effect on the Remaining Useful Life of Bearings Determination and Analysis of Water Content in Lubricating Oils by RH Sensor G. Rowe, Q. Biamonte Arizona Instrument LLC
Lubrication is Essential for Predictive and Preventative Maintenance Lubrication reduces friction, minimizes wear and tear on moving parts,
decreases the likelihood that particle contamination will occur and helps
maintain lower operating temperatures, all of which helps keep your machinery
in optimum operation condition and extend its useful life.
Lubrication is particularly important in regard to bearings. Bearings are the
joints of a machine. They bear heavy loads and help execute and control the
movement of the connected parts. When these joints fail, movement becomes
less fluid and efficient and can eventually cause serious damage. Lubrication is
a machine’s method of protecting its joints and ensuring that the machine as a
whole is in good working order. It creates a barrier between the softer material
of the bearings and the other parts of the machine. This helps defend the bearings against the excessive wear and tear
that can dramatically reduce their useful life.
When something threatens the potential effectiveness of lubrication, it not only affects the lubricant itself, but also the
bearings and other moving parts that it was meant to protect. While each lubricant is designed with a specific purpose
and application in mind, they all share a common nemesis: moisture contamination. This paper will discuss the dangers of
moisture contamination, its effect on bearing life and the various techniques available for moisture analysis.
Different Bearings Require Different Types of Lubrication The most common methods of lubrication associated with bearings are
hydrodynamic and elastohydrodynamic.[2] An understanding of how these types of
lubrication work will help demonstrate the important role that lubrication plays in
ensuring that your machinery continues to run smoothly.
Both hydrodynamic and elastohydrodynamic lubrication use the motion of moving
machinery parts to force the lubricant around or between those moving parts.[4] In
hydrodynamic lubrication specifically, the lubricant is pushed up and around the
bearing, surrounding it in a thin layer of oil. The continued motion of the machinery
allows for a constant flow of lubricating oil, creating a protective layer that is always
This coating prevents the surfaces of the bearings and other machinery parts from
rubbing against one another. Without lubrication, small particulates would break
off, cause particle contamination and increase abrasion. As more particulates break
off, the rate of destruction increases exponentially, damaging both the bearing and
the machinery as a whole.
In elastohydrodynamic lubrication, the lubricant flows between two contact
surfaces. As flow pressure increases, the lube creates a film that completely
separates the two surfaces.[3] This is especially important because the softer
material of the bearing itself is more vulnerable to abrasion. The lubricating oil
provides an extra layer of cushioning that protects bearings and other moving parts
from excessive wear and tear.
Moisture Decreases Lubricant Efficiency and Causes Early Wear and Tear on Machinery Parts Hydrodynamic and elastohydrodynamic lubrication methods are both at risk of
failing when exposed to moisture contamination.[2] Not only does moisture
decrease lubricant efficiency and causes early wear of machinery parts, it also
increases maintenance costs and down-time while machinery is being repaired
and can have devastating effects on the lubricating oils themselves.
Whether from condensation due to temperature fluctuations during storage or
from exposure to ambient humidity, the threat of water contamination is always
there. From base oil to full synthetic, oil’s high susceptibility for water
absorption increases the likelihood that moisture contamination will occur.
Water also renders some additives ineffective while it reacts with others to
create excess sediment, hydrogen sulfide and other compounds.[5] All of this leads to pitting and particle contamination,
which in turn increase friction and decrease performance, reducing bearing life even further.[5]
Water can also cause premature breakdown of a lubricant itself through oxidation and additive precipitation.[9] Moisture
contamination can also change the viscosity of an oil. Excess water lowers an oil’s viscosity, negatively impacting the
lubricant’s ability to maintain the proper film thickness to protect the bearings and ultimately decreasing the load that
those bearings can support.[9] When this happens, corrosion and pitting are more likely to occur. This again leads to particle
contamination and further machinery damage.
As little as 100 ppm water can cause a 32-48% decrease in bearing life.[1] For this reason, it is essential to perform routine
moisture testing on lubricating oils. Not only does this ensure that they are in optimum operating range, but it also helps
to discover, correct and prevent moisture contamination problems before they cause costly or irreparable damage.
Historical Methods of Moisture Analysis Traditional methods for determining the presence of water in oils include the crackle (scintillation) test, Fourier transform
infrared (FTIR) spectroscopy and Karl Fischer (KF) titration.[5] Of these options, only FTIR and Karl Fischer can give
quantitative data regarding the actual moisture content of an oil.
analyzers have a comparable lower detection limit to
that of the KF (10 ppm) but are as easy to use as the
crackle test.[5] No guessing, no hazardous chemicals,
no fragile and expensive glassware and no specialized
training needed.
The RH method allows for a much more simplified
user experience. This decreases the chance of user
error and increases the reliability of test results.
Maintenance is also much less complicated. A yearly
calibration is virtually all that is needed to keep your
analyzer in working order. Because relative humidity sensors are moisture specific, there are also far fewer interferences.
The mercaptans that cause so much trouble in a Karl Fischer have no effect on the results of a relative humidity sensor
moisture analyzer, although methanol and acetonitrile can cause a slight interference when present in high
concentrations.
Comparing Moisture Analysis Test Methods Testing lubricating oils for moisture contamination is essential, but which method is ideal? The crackle test is simple to
perform, but any data gathered is subjective and non-quantitative. FTIR is more sensitive than the crackle test but is prone
to erroneous readings due to its many interferences. That leaves Karl Fischer titration and relative humidity sensing
technology.
For years Karl Fischer has been the gold standard for moisture analysis. Technicians with the proper training and education
are able to obtain accurate and repeatable results. If, however, the relative humidity sensor could be proven to be
equivalent to KF, it could revolutionize how we test for moisture contamination in lubricating oils. An RH sensor moisture
analyzer requires much less upkeep and is durable enough that it can be used not just in the lab, but on the production
floor.
In order to prove the RH sensor moisture analyzer’s equivalence to
KF titration, six lubricating oils with varying levels of moisture
contamination were tested. All were tested using volumetric KF
titration as well as the moisture analyzer with a built-in relative
humidity sensor.
The moisture analyzer used for this experiment consists of an RH
sensor with two plates that have a constant dielectric difference
between them. When moisture travels between the plates, it
changes the capacitance. That change is then used to calculate the
